Asynchronous Transfer Mode (ATM) is a cell-oriented switching and multiplexing technology that uses fixed length cells to carry different types of traffic. Digital Subscriber Line (DSL) technology and its variations use ATM to bring high-bandwidth information to homes and businesses over ordinary copper telephone lines. Variations of DSL technology include: Asymmetric Digital Subscriber Line (ADSL), High bit-rate Digital Subscriber Line (HDSL) and Rate-Adaptive Digital Subscriber Line (RADSL).
ADSL is used for transmitting digital information at high bandwidths using existing phone lines. ADSL technology is asymmetric because most of the channel is used for transmitting information to the user while only a small part of the channel is used for receiving information from the user. ADSL accommodates analog (voice) information simultaneously with the digital transmission of information. ADSL is generally offered at data rates from 512 Kbps to about 6 Mbps.
Most DSL technologies require the installation of a signal splitter at a home or business which requires a visit by the phone company, and therefore an additional expense. G.Lite (also known as DSL Lite, splitterless ADSL and Universal ADSL) is a slower ADSL which splits the line remotely for the user at the telephone company and does not require splitting the line at the user end. G.Lite has initially been approved as a standard by the Telecommunication standardization section of the International Telecommunication Union (ITU-T). The ITU-T standard, “Transmission Systems and Media, Splitterless Asymmetric Digital Subscriber Line (ADSL) Transceivers”, Draft G.992.2, Oct. 12, 1998, (hereafter, “G.Lite standard”) is incorporated by reference herein.
The G.Lite standard specifies power management by defining states for the ADSL Terminal Units (ATUs). The states include an idle state in which no signal is transmitted on the link between the Central Office ATU (ATU-C) and remote ATUs (ATU-Rs). To save power, any ATU can initiate the transition to the idle state. In non-idle states, data is transmitted using ATM cells over the ADSL link. However, in the idle state, no data (including idle cells) are transmitted over the ADSL link. When a cell that is coming from the network needs to go to an ATU-C that is in an idle state, that cell will be dropped because the ATU-C is in an idle state and there is currently no mechanism for waking up the ATU-C when data is coming from the network. Thus, a need exists for a system that allows for G.Lite power management (e.g., an idle state), yet does not lose ATM cells.